Polycystin-1 (PC1), the protein product of the gene most commonly mutated in ADPKD, is part of a receptor/ion channel signaling complex that is thought to be involved in maintaining cellular differentiation. Recently, PC1 was shown to have a primary cilium-based mechanosensory role in renal epithelial cells. We have preliminary data suggesting that antioxidant response element (ARE)-regulated genes are targets of PCI-mediated signaling through the activation of NF-E2 related factor-2 (Nrf2) transcription factor. Nrf2/ARE-regulated gene products constitute the cell's primary defense against endogenous oxidants and exogenous toxicants, protecting cells from the increased proliferation, damage, or death that can be caused by unresolved oxidant stress. We have found that the expression of a number of ARE-regulated genes is reduced in kidneys from homozygous and heterozygous Pkd1 null mice, that the C-tail of PC1 can constitutively signal to upregulate the activity of an ARE reporter gene, that human ADPKD cells display increased proliferation and apoptosis in response to an oxidant stress, and that fluid flow induces expression of ARE-regulated genes in ciliated renal epithelial cells. Taken together, these observations suggest that PC1 has a novel role in general cytoprotection by upregulating protective Nrf2/ARE gene expression. Our overall hypothesis is that deficiency of PC1 results in impaired antioxidant protection that contributes to the dysregulated cell proliferation and apoptosis associated with PKD. The major goals of this proposal are to establish that cells deficient in PC1 have reduced antioxidant protection and are more susceptible to oxidant-induced damage, proliferation and apoptosis. Utilizing renal epithelial cell lines from human ADPKD kidneys and from a Pkd1 null mouse model, we will determine: (1) if PC1-deficient renal epithelial cells have reduced ARE-regulated gene expression and are more prone to oxidant-induced damage;(2) if PC1-deficient renal epithelial cells are susceptible to oxidant-induced proliferation and apoptosis;and (3) if fluid shear stress protects renal epithelial cells from oxidant-induced proliferation, damage and apoptosis. The knowledge gained from these studies will provide new insights into the pathological mechanism of PKD and will provide new therapeutic avenues for the treatment of PKD.